Typically, anti-spam systems make decisions on incoming email messages based on an originating internet protocol (IP) address. The decisions are based on the history of the IP address or the lack of a history for the IP address. Once a decision is made, the email message is either delivered to the user's inbox or appropriately catalogued as spam or as some other undesirable email message. Any information discovered about the IP address after the message is delivered is used to build the reputation of the IP address. For example, the reputation of the IP address may be based on user complaints, feedback loops or other sources. This reputation information is not used to catalogue previously delivered email messages, but is used to catalogue subsequently received email messages from the IP address.